In a large-sized LED (light emitting diode) display apparatus, a plurality of LEDs each emitting a primary color (red, green, blue) are arranged in dot matrix format. Each element on this display apparatus is one LED emitting any one color of red, green, and blue. However, an element size of one LED is large. Even if the display apparatus is large-sized, high definition of the display cannot be realized, and the spatial resolution is not high. Accordingly, in case of inputting an image signal having a resolution higher than a resolution of the display apparatus, reduction or down-sampling of the image signal is necessary. In this case, image quality falls because of flicker caused by aliasing. In order to remove the flicker, the image signal is generally processed through a low-pass filter as a pre-filter. However, if a high region of the image signal is reduced too much, the image somewhat blurs and visibility falls. Furthermore, the spatial resolution is not originally so high. Accordingly, if the aliasing is suppressed by the low-pass filter, the image is apt to blur.
On the other hand, in the LED display apparatus, a response characteristic of a LED element is very quick. Furthermore, in order to maintain brightness, the same image is normally displayed by refreshing a plurality of times. For example, a frame frequency of the input image signal is normally 60 Hz while a field frequency of the LED display apparatus is 1000 Hz. In this way, low resolution and high field frequency are characteristic of the LED display apparatus.
A high resolution method of the LED display apparatus is disclosed in Japanese Patent No. 3396215. In this method, each lamp (LED element) of the display apparatus corresponds to each pixel of image data of one frame. The one frame is divided into four fields (Hereinafter, sub-field) and displayed.
In a first sub-field, each lamp is driven by the same color component as the lamp in color components (red, green, blue) of a pixel corresponding to the lamp. In a second sub-field, each lamp is driven by the same color component as the lamp in color components of a pixel to the right of the corresponding pixel. In a third sub-field, each lamp is driven by the same color component as the lamp in color components of a pixel to the right and below the corresponding pixel. In a fourth sub-field, each lamp is driven by the same color component as the lamp in color components of a pixel below the corresponding pixel.
Briefly, in the method of this publication, the image data is quickly displayed by sub-sampling in time series. As a result, all the image data is displayed.
However, in this method, image data generated by partially omitting pixels of an original image is displayed as an image of each sub-field. Accordingly, the image of each sub-field includes a flicker and a color smear because of aliasing. As a result, in an image displayed for one frame period, the image quality falls because of aliasing.